Tailwind Theme Builder

Set up a fully themed Tailwind v4 + shadcn/ui project with dark mode. Produces configured CSS, theme provider, and working component library.

Workflow

Step 1: Install Dependencies

pnpm add tailwindcss @tailwindcss/vite
pnpm add -D @types/node tw-animate-css
pnpm dlx shadcn@latest init

# Delete v3 config if it exists
rm -f tailwind.config.ts

Step 2: Configure Vite

Copy assets/vite.config.ts or add the Tailwind plugin:

import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'
import tailwindcss from '@tailwindcss/vite'
import path from 'path'

export default defineConfig({
  plugins: [react(), tailwindcss()],
  resolve: { alias: { '@': path.resolve(__dirname, './src') } }
})

Step 3: Four-Step CSS Architecture (Mandatory)

This exact order is required. Skipping steps breaks the theme.

src/index.css:

@import "tailwindcss";
@import "tw-animate-css";

/* 1. Define CSS variables at root (NOT inside @layer base) */
:root {
  --background: hsl(0 0% 100%);
  --foreground: hsl(222.2 84% 4.9%);
  --primary: hsl(221.2 83.2% 53.3%);
  --primary-foreground: hsl(210 40% 98%);
  /* ... all semantic tokens */
}

.dark {
  --background: hsl(222.2 84% 4.9%);
  --foreground: hsl(210 40% 98%);
  --primary: hsl(217.2 91.2% 59.8%);
  --primary-foreground: hsl(222.2 47.4% 11.2%);
}

/* 2. Map variables to Tailwind utilities */
@theme inline {
  --color-background: var(--background);
  --color-foreground: var(--foreground);
  --color-primary: var(--primary);
  --color-primary-foreground: var(--primary-foreground);
}

/* 3. Apply base styles (NO hsl() wrapper here) */
@layer base {
  body {
    background-color: var(--background);
    color: var(--foreground);
  }
}

Result: bg-background, text-primary etc. work automatically. Dark mode switches via .dark class — no dark: variants needed for semantic colours.

Step 4: Set Up Dark Mode

Copy assets/theme-provider.tsx to your components directory, then wrap your app:

import { ThemeProvider } from '@/components/theme-provider'

ReactDOM.createRoot(document.getElementById('root')!).render(
  <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
    <App />
  </ThemeProvider>
)

Add a theme toggle:

pnpm dlx shadcn@latest add dropdown-menu

See references/dark-mode.md for the ModeToggle component.

Step 5: Configure components.json

{
  "tailwind": {
    "config": "",
    "css": "src/index.css",
    "baseColor": "slate",
    "cssVariables": true
  }
}

"config": "" is critical — v4 doesn't use tailwind.config.ts.

---

Critical Rules

Always:

• Wrap colours with hsl() in :root/.dark
• Use @theme inline to map all CSS variables
• Use @tailwindcss/vite plugin (NOT PostCSS)
• Delete tailwind.config.ts if it exists

Never:

• Put :root/.dark inside @layer base
• Use .dark { @theme { } } (v4 doesn't support nested @theme)
• Double-wrap: hsl(var(--background))
• Use @apply with @layer base classes (use @utility instead)

---

Common Errors

Symptom	Cause	Fix
bg-primary doesn't work	Missing @theme inline	Add @theme inline block
Colours all black/white	Double hsl() wrapping	Use var(--colour) not hsl(var(--colour))
Dark mode not switching	Missing ThemeProvider	Wrap app in <ThemeProvider>
Build fails	tailwind.config.ts exists	Delete the file
Animation errors	Using tailwindcss-animate	Install tw-animate-css instead
@apply fails on custom class	v4 breaking change	Use @utility instead of @layer components

See references/common-gotchas.md for detailed error explanations with sources.

---

Asset Files

Copy from assets/ directory:

• index.css — Complete CSS with all colour variables
• components.json — shadcn/ui v4 config
• vite.config.ts — Vite + Tailwind plugin
• theme-provider.tsx — Dark mode provider
• utils.ts — cn() utility

Reference Files

• references/common-gotchas.md — 8 documented errors with GitHub sources
• references/dark-mode.md — Complete dark mode implementation
• references/architecture.md — Deep dive into 4-step pattern
• references/migration-guide.md — v3 to v4 migration